The general approach in the field of track-while-scan radar systems has been to designate and scan a search sector. Some systems do this by employing two orthogonally mounted scanning antennas. Each antenna may radiate a beam which is 10.degree. wide in one direction and 2.degree. wide in the other, and scan a search sector 20.degree. wide. Scanning generally is accomplished by electro-mechanically shifting the antenna beam while the antenna remains stationary, rather than by physically oscillating the antenna. The scans are unidirectional, i.e. when the beam reaches the right-hand end of its scan sector it is blanked and flies back to the left side to start the scan again. The usual scanning rate is 16 times/sec during which the beam may be energized for 50 milliseconds and blanked for 12.5 milliseconds during flyback. The location of an aircraft in the radar scan sector can be determined by measuring the time required for the main beam to scan from the edge of the scan sector to the aircraft.
Many systems are capable of engaging only one target at a time. In one particular system, operating doctrine requires that the radar operators align the target in the center of the scan sector. The operators rotate hand wheels which control the antenna array and move ;he scanned sector so that the target return signal is maintained at the sector center. With regard to tracking, an automatic angle tracking circuit provides only for automatic tracking within the scanned sector. The antenna is not slaved automatically, therefore the angle tracking operators must position the antenna manually to keep the target at the center of the scanned sector.